Secondary piston stop-wire retainer ring

ABSTRACT

A novel stop for the secondary piston of a split master cylinder is disclosed. The stop includes a radially expandable, circumferentially extending portion received in a circumferentially extending groove provided in the secondary fill port of the master cylinder and another portion extending coaxially with the axis of the port that projects into the master cylinder bore. Movement of the secondary piston past the portion of the piston stop that projects into said bore is thereby prevented.

0 United States Patent [151 3,646,759

Hughes et a1. Mar. 7, 1972 [54] SECONDARY PISTON STOP-WIRE 3,040,5366/1962 Werner ..60I54.6

RETAINER RING 1,377,407 5/1921 Depew ,874 39 G f h ..60 54. 72Inventors: Harold w. Hughes; Paul B. Shutt, both of 2 163 6/19 l 6Joseph Primary Examiner-Edgar W. Geoghegan [73] Assignee: The BendixCorporation Assistant Examiner-A. M. Zupcic Att0rneyl(en C. Decker andFlame, l-lartz, Smith and [22] Filed. Aug. 7, 1970 Thompson [21] Appl.No.: 61,884

[57] ABSTRACT [52] US. Cl. ..60/54l.6 R, 60/54.6 E, 251/284 A novel stopfor the secondary piston of a split master cylinder [5 5 is disclosedThe stop includes a expandable circum- [58] Field of Search ..60/54.5 E,54.6; 92/15, 26, feremiany extending portion received in a i f i u 792/85; 251/284 extending groove provided in the secondary fill port ofthe master cylinder and another portion extending coaxially with [56]References C'ted the axis of the port that projects into the mastercylinder bore. UNITED STATES PATENTS Movement of the secondary pistonpast the portion of the piston stop that projects into said bore isthereby prevented. 3,165,896 1/1965 Baldwin ..60/54.6 E 3,250,074 5/1966Blondiau ..60/54.6 4 Claims, 2 Drawing Figures SECONDARY PISTONSTOP-WIRE RETAINER RING BACKGROUND OF THE INVENTION This inventionrelates toa piston stop for use in an automotive split system mastercylinder.

For safety, it has become customary to provide a piston stop to limitreturn movement of the secondary piston in a split master cylindertoward the open end of the bore. One common design provides a bolt whichprojects through the lower portion of the bore. This design requiresthatthe bore of the master cylinder be made substantially longer thanwould otherwise be necessary. Another common design provides a stop thatextends from the master cylinder reservoir through the top of the bore.This design requires that an extra opening be provided to provide asufficient fluid flow area between the reservoir and the bore.

SUMMARY OF THE INVENTION Therefore, an important object of my inventionis to reduce the length of a master cylinder.

Another important object of my invention is to provide a singlepassageway between the reservoir and the bore of the master cylinder inlieu of the two openings presently required in many existing designs.

A further object of my invention isv to. reduce the time required tomachine and assemble master cylinders.

A still further object of my invention is to facilitate disassembly ofthe master cylinder.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinalcross-sectional view of a master cylinder made pursuant to the teachingsof my present invention; and

FIG. 2 is an enlarged cross-sectional, detailed view of that portion ofFIG. 1 enclosed by the dashed lines.

DETAILED DESCRIPTION Referring now to the drawings, a master cylinderincludes a housing 12 defining a bore 14 therewithin and furtherincluding an annular wall 16 defining a reservoir therein. A partition18 divides the reservoir into a pair of compartments 20 and22. A primarycompensating port 24 and a primary fill port 26 communicate thecompartment 20 with the right end portion (viewing FIG. 1) of the bore14. Similarly, a secondary compensating port 28 and a secondary fillport 30 communicate the other compartment 22 with the other end of thebore 14.

The bore 14 includes an open end 32 and a closed end'34. An annular ring36 circumscribes the bore 14 adjacent the open end 34. A primary piston38 is slidably disposed in the bore 14 and one end of piston 38 isnormally urged into engagement with the ring 36. A secondary piston 40is slidably disposed within the bore 14 between the other end of thepiston 38 and the closed end of the bore. A first fluid chamber '42isdefined between the two pistons 38 and 40, and a second fluid chamber 44is defined by the end of the piston 40 and the closed end 34 of the bore14. Chamber 42 is communicated to the rear brakes of the vehicle throughoutlet port 43 and chamber 44 is communicated to the front brakes of thevehicle through outlet port 45. A caged spring assembly 46 is disposedbetween the pistons 38 and 40, and another spring 48, which has a lowerspring constant than does the caged spring assembly 46, is disposedbetween the end of piston 46 and the closed end 34 of the bore 14. A cap50 and bladder 52 seal the open upper ends of the compartments 20 and22.

The piston 40 is provided with larger diameter sections 54, 56 and asmaller diameter section 58 therebetween that cooperates with thesection 54 to define a transversely extending shoulder 60 therebetween.The smaller diameter section 58 cooperates with the wall of the bore 14to define an annular cavity 62 therebetween. Appropriate seals 64, 66seal the piston against the wall of the bore 14. The primary piston 38is of similar construction.

Referring now to FIG. 2, the secondary fill port or fluid passage 30 isprovided with a circumferentially extending groove 68. A piston stop 70is formed from a length of wire and includes a circumferentiallyextending portion 72 and a transversely extending portion 74. Thecircumferentially extending portion is radially resilient so that it canbe compressed forinsertion into the port 30, and then can expandradially to forcibly engage the sides of the groove. The transverselyextending portion 74 extends generally coaxially with the fluid passage30, and has a diameter substantially smaller than that of the passage 30so that fluid communication between the compartment 22 and the bore 14is not substantially impeded.

MODE OF OPERATION When the vehicle brakes are released, the pistons 38and 40 are disposed within the bore 14 in the position illustrated inFIG. 1. When the vehicle operator depresses the brake pedal mounted inthe operator's compartment, the piston 38 and 40 move to the leftviewing FIG. 1 thereby pressurizing the fluid in the chambers 42 and 44to apply the vehicle brakes in a manner well known to those skilled inthe art. It should be noted that when the pistons 38 and 40 are disposedin the brake-released position, the shoulder 60 does not engage thetransversely extending portion 74 of the piston stop 70 that projectsinto the bore 14. However, under certain conditions of operation, suchas when the vehicle brakes are applied and released a number of times insuccession, the respective pressure levels in the chambers 42 and 44 aresuch that a force is exerted on. the piston 40 urging it toward the openend of the bore 14. If no piston stop is provided, the seal 64 will bedamaged when it moves past the fill port 30. However, in the deviceillustrated in the Figures, the transversely extending portion 74 on thepiston stop 70 engages the shoulder 60 to limit movement of the piston40 toward the right viewing the figures. Also, when the brakes areapplied and released a number of times in succession, a void is createdin the chamber 44 because the brake fluid does not return from the brakelines quickly enough. Therefore, fluid is pulled into the chamber 44from the annular cavity 62 past the seal 64. This fluid. must be quicklyreplenished from the fluid stored in the compartment 22. Since thediameter of the transversely extending portion 74 of the piston stop 70is substantially smaller than the cross-sectional area of the fill port30, flow of fluid between the. compartment 22 and the cavity 62 is notsubstantially impeded.

What is claimed is:

1. In a fluid motor:

a housing defining a bore therewith;

a piston slidable in said bore;

said piston being stepped to present a larger diameter portion slidablyengaging the wall of said bore and a smaller diameter portion, saidlarger and smaller diameter portions defining a shoulder therebetween;

said housing having an annular wall defining a reservoir therewithin;

a passage communicating the reservoir with the bore; and

a piston stop having a circumferentially extending annular portionengaging the wall of said passage and another portion extending throughsaid passage into said bore for engagement by said shoulder said anotherportion being spaced from the wall of said passage and havingcross-sectional area substantially smaller than the cross-sectional areaof the passage to permit substantially uninhibited flow through saidpassage.

2. The invention of claim 1; and

a circumferentially extending groove in the wall of said passage;

said groove receiving said circumferentially extending annular portionto thereby retain said piston stop within said passage.

3. The invention of claim 2:

said annular portion being expandable in a radial direction whereby thelatter forcibly engages the walls of said groove.

4. The invention of claim 1:

said annular portion being expandable in a radial direction 5 wherebythe latter forcibly engages the wall of the passage.

k i t t

1. In a fluid motor: a housing defining a bore therewith; a pistonslidable in said bore; said piston being stepped to present a largerdiameter portion slidably engaging the wall of said bore and a smallerdiameter portion, said larger and smaller diameter portions defining ashoulder therebetween; said housing having an annular wall defining areservoir therewithin; a passage communicating the reservoir with thebore; and a piston stop having a circumferentially extending anNularportion engaging the wall of said passage and another portion extendingthrough said passage into said bore for engagement by said shoulder,said another portion being spaced from the wall of said passage andhaving cross-sectional area substantially smaller than thecross-sectional area of the passage to permit substantially uninhibitedflow through said passage.
 2. The invention of claim 1; and acircumferentially extending groove in the wall of said passage; saidgroove receiving said circumferentially extending annular portion tothereby retain said piston stop within said passage.
 3. The invention ofclaim 2: said annular portion being expandable in a radial directionwhereby the latter forcibly engages the walls of said groove.
 4. Theinvention of claim 1: said annular portion being expandable in a radialdirection whereby the latter forcibly engages the wall of the passage.